This invention relates to an Electromagnetic Interference (hereinafter "EMI") gasket used for shielding electromagnetic or electrostatic interference through openings of a casing of an electronic device, and more particularly for shielding openings from which optical fibers are inserted in an optical communication apparatus.
Examples of heretofore used shielding devices are shown in FIG. 1 and FIG. 2. An optical fiber introduction in a casing shown by FIG. 1 is disclosed in a Japanese Utility Model Publication No. 1912/'90. Optical fibers 25 are inserted into a casing 21 through tubular conductors 22 and 23 connected to the casing 21. Diameters and lengths of these conductor tubes 22 and 23 are so determined as to prevent electromagnetic waves from entering casing 21 through the openings surrounding these conductor tubes.
In an example shown in FIG. 2, a gap 38 which is formed between a casing body 36 and a front panel 37 is also shielded by an EMI gasket 31 comprising an inner buffer member 32 and an outer conductive coating 33.
The inner diameters of the tubular conductors 22 and 23 are small for increasing shielding effect, and an optical fiber can barely pass through the inner diameter. Sometimes, it is very difficult to pass an optical fiber through the conductor. As the tubular conductors are made of metal, optical fibers may be damaged by the tubular conductors when external forces are improperly applied to the optical fibers. A tubular conductor is necessary for each optical fiber, raising total manufacturing cost of the casing. The EMI shield in the gap 38 also increases the production cost.